This invention generally relates to a vehicle occupant restraint system for a three-point seat belt system. More specifically, the invention relates to a system having means for determining if a seat belt is being used properly by an occupant.
It is well known in the art that using a three-point seat belt, in a vehicle, will aid in preventing injury to an occupant. A three-point seat belt system typically comprises a retractor, D-ring or belt guide, a buckle and associated tongue, lower belt restraint anchor and seat belt webbing. Generally, the seat belt webbing (or seat belt) is divided into a lap (belt) portion and a shoulder (belt) portion. The proper or intended use of the seat belt is for the occupant to wear or to install the shoulder belt portion across his upper torso and the lap belt portion across his lap. It is also known that some occupants, for whatever reason, occasionally place the shoulder belt portion belt behind their backs with the lap belt portion buckle about the waist. If the seat belt is utilized in this improper manner the vehicle occupant's upper torso cannot be restrained during a crash event. This improper use of the seat belt will minimize the occupant restraining qualities of the restraint system. This improper use is also important in relation to the operation of a "smart" air bag restraint system which controls the inflation of the air bag during an accident. With the seat belt improperly used the occupant's upper torso, during a crash, will move forwardly into the inflating air bag. With knowledge of the state of use or misuse of the seat belt this information can be used to lower the inflation rate of the inflating air bag or negate the operation of the air bag.
One of the objects of this invention is to provide a system that is capable of determining if an occupant is not wearing the seat belt as it was designed to be used. It is a second object of this invention to provide at a minimum, a warning signal to reinforce to the occupant (or at least to a responsible adult) of improper seat belt use so that the seat belt can be placed properly about the occupant. Finally, it is an object of the present invention to modify the operation of other on-board safety restraint systems, such as an air bag system, based on the state of use or misuse of the seat belt.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.